Crystal matrix protein--getting blood out of a stone

The short history of crystal matrix protein began in 1991, when it was shown to be the predominant protein present in the organic extract of calcium oxalate crystals precipitated from fresh human urine. Here, we review what has subsequently come to be known about the protein, from its highly specific immunohistochemical distribution in the human nephron, to its finding in kidney stones, to the discovery of its relationship with the human blood coagulation zymogen prothrombin, and, finally, its identification as a urinary form of prothrombin activation fragment 1. A vitamin K-dependent glycopeptide, fragment 1 possesses the so-called GLA domain of its parent molecule; its known properties suggest that it may fulfil a determinant role in calcium oxalate urolithiasis as a potent urinary inhibitor of crystal growth and aggregation.